Multi-stage centrifugal pump

ABSTRACT

The invention relates to a multi-stage centrifugal pump with a foot part ( 2 ), a head part ( 14 ) and a wall part ( 16, 16 ′) which connects the foot part ( 2 ) to the head part ( 14 ) and which peripherally surrounds the pump stages at the outer periphery. The centrifugal pump moreover comprises a motor stool connecting to the head part ( 14 ) and for receiving an electric motor ( 20 ) provided for the drive of the centrifugal pump. The wall part ( 16 ) projects in the axial direction beyond the head part ( 14 ) and is connected to the motor stool (FIG.  1 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119 ofEuropean Patent Application 15 164 219.6 filed Apr. 20, 2015, the entirecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a multi-stage centrifugal pump with multi-stagecentrifugal pump with a foot part, a head part, a wall part whichconnects the foot part to the head part and surrounds the pump stages atthe outer periphery, and with a motor stool connecting to the head partand for receiving an electric motor provided for the drive of thecentrifugal pump.

BACKGROUND OF THE INVENTION

Centrifugal pumps as are known for example from the pump constructionseries CR and CRE of the company Grundfos, form the starting point ofthe invention. Hereby, it is the case of multi-stage, verticallyoperated centrifugal pumps, with which at least two pump stages arearranged in a pump casing between a foot part and a head part of thepump casing, and are surrounded at the outer periphery by a wall partconnecting the foot part to the head part. A suction branch and adelivery branch of the centrifugal pump are formed on the foot part. Thefluid to be delivered by the centrifugal pump gets through the suctionbranch firstly into a first pump stage and from there further to thelast pump stage, from where it is again led back again into the footpart and there is led out of the centrifugal pump via the deliverybranch. The pump shaft of the centrifugal pump which connects theimpellers of the individual pump stages, is led out through the headpart in a sealing manner, where it is coupled in movement to the motorshaft of an electrical drive motor which is mounted on a motor stooltypically formed from cast steel, in a manner distanced axially to thehead part. With regard to the known centrifugal pumps, the motor stoolis either an integral constituent of the head part or is releasablyfastened on the head part, wherein rod bolts connect the motor stool tothe foot part.

SUMMARY OF THE INVENTION

It is an object of the invention to create a multi-stage centrifugalpump of the previously described type which compared to known pumps hasa simplified construction and a more attractive appearance.

The multistage centrifugal pump according to the invention comprises ahead part and a foot part, between which at least two pump stages eachwith an impeller are arranged. With regard to this centrifugal pump, itis preferably the case of a vertically operated centrifugal pump, whichis to say a centrifugal pump which is operated standing on the foot partand with vertically aligned impeller axes, but it is to be noted thatwith regard to the centrifugal pump according to the invention, it canalso be the case of a centrifugal pump operated in any other position.The pump stages of the centrifugal pump are surrounded at the outerperiphery by a wall part which connects the foot part to the head partand thus together with the foot part and the head part forms a pumpcasing. The centrifugal pump according to the invention moreovercomprises a motor stool which connects to the head part and is forreceiving an electric motor provided for operation of the centrifugalpump. The electric motor is mounted on the motor stool in a mannerdistanced to the head part in the direction of the middle axis of thecentrifugal pump, wherein an end of a pump shaft connected to theimpellers of the pump stages and which projects out of the head part canbe coupled to a motor shaft of the electric motor in the region of themotor stool.

Compared to the known multistage centrifugal pumps of the type beingdiscussed here, the centrifugal pump according to the invention ischaracterized in that the wall part of the pump casing extends beyondthe head part in the axial direction, which is to say in the directionof the middle axis of the centrifugal pump or in the direction of itsimpeller axes, and is connected to the motor stool for receiving theelectric motor. In contrast to conventional centrifugal pumps, with thecentrifugal pump according to the invention, it is thus no longer thehead part but instead it is the wall part which surrounds the pumpstages of the centrifugal pump at the outer periphery which carries themotor stool. The fashioning freedom with regard to the design of thecentrifugal pump is increased to a significant extent by way of this.This for example relates to the design of the head part which can besimplified with regard to design and manufacturing technology due to itsstatic loading which is significantly reduced in comparison to the knowncentrifugal pumps. The rod bolts which have hitherto been used for theconnection of the motor stool to the foot part are no longer requiredwith the centrifugal pump according to the invention. Completely newpossibilities also result with regard to the overall optical appearanceof the centrifugal pump, so that the centrifugal pump can be designed inan optically more pleasing manner.

The wall part is preferably formed by a tube, in which the head part isintegrated, which is simple with regard to design and manufacturingtechnology. With regard to the tube, it can either be the case of a tubewith a welded seam or a seamless tube. In the latter case, the tube canbe manufactured for example by way of deep-drawing, by which means thewall thickness of the wall part can be easily determined. The tube,independently of its design, at one end is usefully connected to thefoot part in a pressure-tight manner. The head part, in a section of thetube which is adjacent to the other end of the tube, is inserted at adistance to this end and is likewise connected to the tube in apressure-tight manner. The head part is preferably welded in the tube inthis position. Hereby, the welding connection of the head part and thetube can be provided within the tube, or the weld connection can becarried out from the outer side of the tube.

The motor stool preferably comprises an annular flange which is arrangedat the end of the section of the wall part which extends beyond the headpart. The annular flange is advantageously an aluminum injection moldedpart, as is preferably also the complete motor stool. The radialdimensions of the annular flange are preferably such that the outerperiphery of the annular flange is aligned to the outer periphery of thewall part, so that the annular flange extends radially only into theclearance or in the direction of the inside of the wall part, but at theouter side does not project beyond the outer periphery of the wall part.

Further advantageously, the annular flange is configured in a shoulderedmanner, wherein it comprises a section engaging into the inside of thewall part, and a section lying on the end of the wall part. Hereby, theouter diameter of the section engaging into the inside of the wall partusefully corresponds to the inner diameter of the wall part, so that thewall part at its free end which is away from the foot part can besupported in the radial direction on the section engaging into theinside of the wall part, which gives the section of the wall part whichforms the motor stool an increased stability.

The annular flange advantageously forms the complete motor stool. Inthis context, a design, with which the annular flange is configured forfastening the electric motor is preferred. The electric motor is herebymounted on the flat side of the annular flange which is away from thefoot part. The fastening of the electric motor on the annular flange isusefully effected in the region of the annular flange which extends intothe clearance of the wall part, where the fastening means on the annularflange side are preferably arranged for fastening the electric motor onthe annular flange. Hereby, it is preferably the case of through-holeswhich serve for receiving screws, with which the electric motor isscrewed to the annular flange.

According to a further preferred design of the centrifugal pumpaccording to the invention, the annular flange is configured forfastening different electric motors. In this context, it can beadvantageous for several through-holes for creating a screw connectionto a counter-flange of a first electric motor to be formed on theannular flange at a first radial distance to a middle axis of theannular flange, in a row distributed over the periphery of the annularflange, and for further through-holes for creating a screw connection toa counter-flange of a second electric motor to be provided on theannular flange at least at one second radial distance which is differentto the radial distance of these through-holes, in a manner distributedin a row over the periphery of the annular flange.

With an advantageous design which is alternative to an annular flangeand which directly forms the motor stool, an attachment (addition orextension) which projects in the axial direction and at whose end, whichis away from the annular flange, a fastening flange for the electricmotor is arranged, can be arranged on the annular flange for forming themotor stool. This design has been found to be advantageous for exampleif larger electric motors are used. Moreover, the attachment whichprojects axially on the annular flange permits the section of the wallpart which projects beyond the head part of the centrifugal pump to bedesigned in a comparatively short manner, which has a positive effect onthe bending and torsional stiffness of this section. The fasteningflange which is arranged on the end of the attachment which is away fromthe annular flange, in the case of smaller electric motors can bedimensioned such that it is arranged within the clearance of the wallpart, or with electric motors of a larger construction type or electricmotors with a larger counter-flange than the fastening flange, can alsoproject radially beyond the outer contour of the wall part.

Preferably, at least one window is formed on the section of the wallpart which extends beyond the head part. This window is to be understoodas a larger recess which is provided on the wall part and via which theinside of the wall part is accessible in the region of the sectionforming the motor stool, for maintenance and repair purposes. The atleast one window is thus integrated into the wall part. On dimensioningthe window, one is to take into account the fact that the wall part hasto carry the weight of an electric motor, i.e. the at least one windowwhere possible should have no influence on the mechanical stability ofthe wall part and accordingly should not be too large.

Moreover, the fact that a mechanical weakening of the wall part which iscaused by the at least one window can have an unfavorable effect withregard to an undesirable natural frequency excitation of the wall partshould be taken into account. In order to counteract this, it isadvantageous to increase the stiffness of the wall part by way ofsuitable measures. One step directed toward this can lie in increasingthe wall thickness of the wall part in the section projecting beyond thehead part, with respect to the wall thickness at the remaining wallpart. As a further measure, it is also possible for a cover plate of thewindow to provide a supporting function. Moreover, the mechanicalstructure can also be stabilized by way of suitable mechanicaldeformations being formed in the wall part.

Particularly advantageously, two windows are formed on the section ofthe wall part which extends beyond the head part, and these are arrangedin a manner such that a shaft seal which seals the pump shaft withrespect to the head part, as well as at least one bleed valve of thecentrifugal pump which is arranged on the head part, are accessible viathe windows. Preferably, two bleed valves are provided on the head partwith the centrifugal pump according to the invention, and these arearranged together in a plane running through the middle axis of thecentrifugal pump and its head part, on two sides which are away from themiddle axis. In this case, the two windows formed on the wall part arefavorably arranged lying diametrically opposite one another and radiallyat the outer side of the bleed valves.

The head part of the centrifugal pump according to the invention ispreferably designed as a deep-drawn part of preferably stainless steel.Accordingly, a comparatively thin-walled sheet of steel and preferablyof stainless steel, which is brought into a preferably arched shape byway of a deep-drawing procedure, can be used for the manufacture of thehead part. The head part of the centrifugal pump according to theinvention thus has a significantly reduced weight compared to the headparts which until now have been formed from cast steel, and this alsohas a positive effect on the total weight of the centrifugal pump.Moreover, the corrosion resistance of the head part has-been found to beadvantageous when using stainless steel.

The wall part is connected to the foot part usefully in a releasablemanner for maintenance, cleaning or repair purposes. In this context,one preferably envisages the wall part being clamped on the foot partwith a clamping ring. Hereby, preferably a section of the foot partengages into an end section of the wall part which is away from the headpart and from the motor stool, wherein the clamping ring radiallysurrounding the wall part at the outside presses the wall part againstthe foot part. Hereby, a seal is usefully arranged between the wall partand the foot part, for the pressure-tight sealing of the wall part withrespect to the foot part.

The clamping ring which is used for connecting the wall part to the footpart is preferably designed in a manner divided into several ringsegments in the peripheral or circumferential direction. Accordingly,the clamping ring comprises several ring segments which, arranged nextto one another in the peripheral direction and connected to one another,result in the clamping ring. This divided or split design of theclamping ring is advantageous inasmuch as it permits a simplearrangement of the clamping ring at the outside of the wall part andensures a uniform force transmission from the clamping ring onto thewall part.

The individual ring segments of the clamping ring are preferablydesigned in a manner such that a recess which is directly adjacent therespective end of the ring segment is formed in each case at bothperipheral ends of the individual ring segments, wherein a first recessis formed on a first flat side of the ring segment which is alignedperpendicularly to the middle axis of the clamping ring, and the otherrecess is formed on a second flat side which is away from the first flatside and is aligned parallel to the first flat side. Accordingly, onerecess is directed in the direction of the head part, whilst the otherrecess faces the foot part, in the condition of the ring segmentsassembled on the wall part. The ring segments of the clamping ring whichare connected to one another are arranged overlapping one another in theaxial and peripheral direction of the clamping ring, in the region ofthe recesses.

The individual ring segments of the clamping ring are not only connectedto one another, but preferably in each case also to the foot part. Thus,according to a further advantageous design of the centrifugal pumpaccording to the invention, one envisages the ring segments of theclamping ring being connected to the foot part amid the creation of aconnection to one another. Through-holes which are aligned in the axialdirection of the clamping ring are formed on the two recesses of thering segments for this, and these through-holes are arranged in a mannersuch that in the assembled condition of the clamping ring and with therecesses of the ring segments which then overlap one another, thethrough-holes formed on the recesses overlapping one another are alignedto one another. A cap screw is led through the thus formed commonthrough-hole in each case and is screwed in a threaded pocket holeformed on the foot part.

The invention is hereinafter explained in more detail by way ofembodiment examples which are represented in the drawing—in each case,in a schematically simplified manner and in different scales. Thevarious features of novelty which characterize the invention are pointedout with particularity in the claims annexed to and forming a part ofthis disclosure. For a better understanding of the invention, itsoperating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a lateral view of a vertical multi-stage centrifugal pump;

FIG. 2 is a sectional view along the section line II-II in FIG. 1;

FIG. 3 is a plan view of the centrifugal pump according to FIGS. 1 and2;

FIG. 4 is a perspective representation, an end section of thecentrifugal pump according to FIG. 1-3, in the region of a head part ofthe centrifugal pump;

FIG. 5 is a view in the direction V-V in FIG. 4;

FIG. 6 is a perspective representation, an end section of thecentrifugal pump according to FIGS. 1-3, in the region of a foot part ofthe centrifugal pump;

FIG. 7 is a lateral view of an end section according to FIG. 6;

FIG. 8 is a plan view of a ring segment of a clamping ring;

FIG. 9 is a perspective representation of a ring segment according toFIG. 8;

FIG. 10 is a detail A of FIG. 2;

FIG. 11 is a perspective representation of a pump assembly with acentrifugal pump according to the FIGS. 1-3 and with an electric motorfor the drive of a centrifugal pump;

FIG. 12 is a longitudinal sectional view of an end section ofcentrifugal pump according to a second design in the region of a headpart of the centrifugal pump;

FIG. 13 is a detail of FIG. 12 in a perspective representation;

FIG. 14 is a longitudinal sectional view of an end section of acentrifugal pump according to a third design, in the region of a headpart of the centrifugal pump; and

FIG. 15 is a lateral view of an end section of a pump assembly with acentrifugal pump according to a fourth design.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the multistage centrifugal pump which isrepresented in the FIGS. 1-11 comprises a foot part 2. This foot part 2is equipped with two connection flanges 4 and 6. Of these connectionflanges 4 and 6, the connection flange 4 forms a suction branch and theconnection flange 6 a delivery branch of the centrifugal pump.

The connection flange 4 forming the suction branch surrounds a suctionchannel 8 which runs out within a suction space which is formed in thefoot part 2 and on which the suction port of an impeller 10 of a firstpump stage of the centrifugal pump connects, said pump stage beingformed by the impeller 10 and a casing 12 surrounding this. As a whole,the centrifugal pump comprises five pump stages which consist of animpeller 10 and a casing 12. The pump stages are arranged verticallyabove one another, wherein the impellers 10 of these pump stages areseated on a common pump shaft led out of the pump casing of thecentrifugal pump at its upper side, on a head part 14 distanced to thefoot part 2 in the vertical direction. This pump shaft is of norelevance concerning the invention and has therefore been omitted in thedrawing for the purpose of an improved overview.

The pump casing of the centrifugal pump, apart from the foot part 2 andthe head part 14 is also formed by a wall part 16 which connects thefoot part 2 to the head part 14 and surrounds the pump stages of thecentrifugal pump at a radial distance. A stainless steel tube serves asa wall part 16 in the present embodiment example. As can be deducedparticularly well from FIGS. 1, 4 and 11, the wall part 16 comprises asection 18, which extends in the axial direction of the centrifugal pumpbeyond the head part 14. The head part 14 is thus integrated in the wallpart 16 at a distance to the end of the wall part 16 which is away fromthe foot part 2, wherein the head part 14 is connected to the wall part16 in a pressure-tight manner by way of welding. The welding is carriedout at the inner side of the wall part 16 by way of laser welding.

An annular flange 24 is arranged at the end of the section 18 of thewall part 16, said end being away from the foot part 2. The annularflange 24 forms a motor stool for an electric motor 20, wherein a motorshaft of the electric motor 20 is connected via a coupling 22 to thepump shaft which is not represented, in the region of the section 18 ofthe wall part 16.

It can be recognized from FIG. 2 that the annular flange 24 isconfigured in a shouldered manner and comprises a section 26 whichengages into the inside of the wall part, and a section 28 which lies onthe end of the wall part 16. Hereby, the outer cross section of thesection 26 of the annular flange 24 corresponds to the inner crosssection of the wall part 16 and the outer cross section of the section28 of the annular flange 24 to the outer cross section of the wall part16.

The connection of the electric motor 20 to the annular flange 24 iseffected via a screw connection. For this, four through-holes 30 whichextend in the axial direction of the annular flange 24 are formed on theannular flange 24 at the same radial distance to the center of theannular flange 24 as is particularly evident from FIG. 4, and thesethrough-holes serve for receiving screws, by way of which acounter-flange of the electric motor 20 is fastened on the annularflange 24. Moreover, four further axially directed through-holes 32which are arranged at the same radial distance to the center of theannular flange 24 are formed on the annular flange 24, wherein theradial distance of the through-holes 32 to the center of the annularflange 24 is smaller than the radial distance of the through-holes 30 tothe center of the annular flange 24. The through-holes 32 serve for thefastening of an electric motor whose counter-flange differs from thecounter-flange of the electric motor 20.

Two windows 34 lying diametrically opposite one another are formed onthe section 18 of the wall part 16. The inside of the section 18 of thewall part 16 is accessible from outside the wall part 16 via the windows34. Thus, amongst other things, assembly, maintenance or repair work onthe coupling 22 connecting the pump shaft to the motor shaft as well ason a shaft seal 36 sealing the pump shaft with respect to the head part14, and on two bleed valves 38 of the centrifugal pump which arearranged on the head part 14 can thus be carried out via the windows 34.

Two recesses, into which in each case a tongue 40 directed into theinside of the wall part 16 and serving for the releasable fastening ofthe annular flange 24 on the wall part 16 are formed in each case on anupper side of the window 34 which faces the annular flange 24. Athrough-hole 42 is formed in each case in a region of the tongue 40which covers the section 26 of the annular flange 24, and thisthrough-hole serves for receiving a screw which is screwed into athreaded pocket hole which is formed on the section 26 of the annularflange 24 and corresponds to the through-hole 42 with regard to itsposition, by which means the annular flange 24 is fastened on the wallpart 16.

The wall part 16 is radially widened at its end which is away from thehead part 14, by way of the wall part 16 there merging via a shoulderinto a radially widened section 44. A section 46 of the foot part 2which forms a part of the flow connection between the connection flanges4 and 6 and the pump casing (see FIGS. 2 and 10) engages into thiswidened section 44 of the wall part 16. An annular grove 48 which servesfor receiving a sealing ring 50 sealing the wall part 16 with respect tothe foot part 2 is formed on the outer periphery of the section 46 ofthe foot part 2 (FIG. 2).

The pressure-tight connection of the wall part 16 to the foot part 2 iseffected via a clamping ring 52. This clamping ring 52 is configured ina peripherally divided manner and comprises six identical ring segments54, whose construction is evident from the FIGS. 8 and 9. It can bededuced from FIGS. 8 and 9 that a recess 56 and 58 which is directlyadjacent the respective end of the ring segments 54 is formed on the twoperipheral ends in each case. Hereby, the recess 56 is formed on a flatside 60, and the recess 58 on a flat side which is away from the flatside 60, of the ring segment 54. The ring segments 54 moreover,adjacently the flat side 60, each comprise a shoulder 64 which isdirected in the direction of the center of the clamping ring 52 in theassembled condition of the ring segments 54. The ring segments 54 in theassembled condition overlap one another in the region of the recesses 56and 58 which are formed on the ring segments 54, wherein a section of afirst ring segment 54 which is reduced in the axial direction of theclamping ring 52, in the region of the recess 56, contacts a section ofa second ring segment 54 which is likewise reduced in the axialdirection of the clamping ring 52, in the region of the recess 58.

The connection of the ring sections 54 to one another is effected via ascrew connection. Through-holes 68 are formed on the ring segments 54 inthe region of the recesses 56 and 58, for receiving the screws 66 whichare necessary for this, and these through-holes are aligned to oneanother when adjacent ring segments 54 overlap one another in the regionof the recesses 56 and 58. The screws 66 not only serve for theconnection of the ring segments 54 to one another, but also for clampingthe clamping ring 52 on the outer side of the wall part 16, which isevident from FIG. 10. For clamping the clamping ring 52 on the outerside of the wall part 16, the individual ring segments 54 of theclamping ring 52 are arranged on the outer side of the wall part 16 suchthat with their shoulder 64 they engage around a shoulder 70 which onthe wall part 16 forms a transition to the widened section 44 of thiswall part, and come to bear on six projections 72 projecting radially onthe foot part 2, wherein the through-holes 68 which are formed on thesections of the ring segments 54 which overlap one another are alignedwith threaded pocket holes 74 formed on the projections 72. The screws66 which are led through the through-holes 68 of the ring segments 54are screwed into the threaded pocket holes 74, for clamping the clampingring 52 on the outer side of the wall part 16.

The centrifugal pump which is represented in the FIGS. 12 and 13 differsfrom the centrifugal pump represented in FIGS. 1-11 merely with regardto the design of the wall part connecting the foot part 2 to the headpart 14, as well as with regard to the design of the motor stool and itsconnection to the wall part. With the centrifugal pump represented inFIGS. 12 and 13, a wall part 16′ extends beyond the head part to alesser extent than the wall part 16 of the centrifugal pump representedin FIGS. 1-12, so that a section 18′ of the wall part 16′ is shorterthan the section 18 of the wall part 16 of the centrifugal pumprepresented in FIGS. 1-12.

An annular flange 24′ which engages with a section 26′ into the insideof the wall part 16′ and lies with a section 28′ on the wall part 16′ isarranged at the end of the wall part 16′ which is at the top in FIGS. 12and 13. The annular flange 24′ at its flat side which is away from thehead part 14 comprises an attachment 76. The attachment 76 is formed bytwo webs 78 which are arranged lying opposite one another on the annularflange 24 and taper obliquely to a middle axis X of the centrifugalpump. Of the two webs 78, only one web 78 is visible in each case in theFIGS. 12 and 13.

A fastening flange 80 is arranged on the attachment 76 at the end ofthis which is away from the annular flange 24′. The fastening flange 80serves for fastening an electric motor 20 which is screwed with acounter-flange on the fastening flange 80.

Together, the annular flange 24′, the attachment 76 and the fasteningflange 80 thus form a motor stool for the electric motor 20, wherein thecoupling of the pump shaft to the drive shaft of the motor 20, saidcoupling not being represented in FIGS. 12 and 13 and being arrangedbetween the fastening flange 80 and the annular flange 24′, is easilyaccessible on this motor stool via intermediate spaces between the webs78 forming the attachment 76, as is also the case with the components onthe head part 14 and which are likewise to some extent not represented.

The fastening of the motor stool of the centrifugal pump which isrepresented in FIGS. 12 and 13 is particularly evident from FIG. 13. Tworectangular openings 82 are formed on the wall part 16′, in a mannerlying diametrically opposite one another and just below the region, inwhich the section 26′ of the annular element 24′ engages into the insideof the wall part 16′, in order to fasten the motor stool. The openings82 in each case serve for receiving a fastening element 84. Thefastening elements 84 each comprise a base body 86 with a rectangularcross-sectional contour which corresponds to the openings 82 and whichengages from the outer side of the wall part 16′ through the opening 82into the inside of the wall part 16′, and an end section 88 whichprojects beyond the cross-sectional contour of the base body 86 andcomes to bear on the outer side of the wall part 16′. In each case, athreaded hole 90 which in the installed condition of the fasteningelement 84 on the wall part 16′ is aligned parallel to the middle axis Xof the centrifugal pump extends through the base body 86 of thefastening elements 84. Two through-holes 92 are formed on the annularflange 24′, in a manner corresponding to the position of the threadedhole 90 in the installed condition of the fastening elements 84 on thewall part 16′. These through-holes 92 serve in each case for receiving ahead screw 94 which is screwed into the threaded hole 90 of thefastening element 84, by which means the motor stool is fastened on thewall part 16′.

The centrifugal pump represented in FIG. 14 corresponds essentially tothe centrifugal pump represented in FIGS. 12 and 13 and differs fromthis only with regard to the fastening of the motor stool on the wallpart 16′. This fastening is effected by way of a weld connection of theannular flange 24′ to the wall part 16 in the region, in which thesection 26′ engages into the inside of the wall part 6′.

The centrifugal pump which is represented in FIG. 15 is basedessentially on the centrifugal pump represented in FIGS. 1-11 anddiffers from the latter mentioned centrifugal pump merely with regard tothe design of the motor stool. This motor stool comprises an annularflange 24″ which differs from the annular flange 24 of the centrifugalpump represented in FIGS. 1-11 only with regard to the axial dimensionsof the section 28″. A fastening flange 80′ is arranged on the flat sideof the section 28′ which is away from the wall part 16. The fasteningflange 80′ is configured for fastening electric motors 20 to a largercounter-flange 96 and for this purpose extends radially beyond the outerperiphery of the wall part 16. The fastening flange 80′ in this regionextending beyond the outer periphery of the wall part 16 is supported onseveral reinforcement ribs 98 which project radially on the outerperiphery of the section 28″ of the annular flange 24″.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

APPENDIX List of Reference Symbols

-   2 foot part-   4 connection flange-   6 connection flange-   8 suction channel-   10 impeller-   12 casing-   14 head part-   16, 16′ wall part-   18, 18′ section-   20 electric motor-   22 coupling-   24, 24′, 24″ annular flange-   26, 26′ section-   28, 28′, 28″ section-   30 through-hole-   32 through-hole-   34 window-   36 shaft seal-   38 bleed valve-   40 tongue-   42 through-hole-   44 section-   46 section-   48 annular groove-   50 sealing ring-   52 clamping ring-   54 ring segment-   56 recess-   58 recess-   60 flat side-   62 flat side-   64 shoulder-   66 screw-   68 through-hole-   70 shoulder-   72 projection-   74 threaded pocket-hole-   76 attachment-   78 web-   80, 80′ fastening flange-   82 opening-   84 fastening element-   86 base body-   88 end section-   90 threaded hole-   94 cap screw-   96 counter flange-   98 stiffening rib-   A detail-   X middle axis

What is claimed is:
 1. A multi-stage centrifugal pump comprising: a footpart; a head part; pump stages; an electric motor to drive the pumpstages; a wall part which connects the foot part to the head part andsurrounds the pump stages at an outer periphery; a motor stool connectedto the head part and receiving the electric motor, wherein the wall partprojects in an axial direction beyond the head part and is connected tothe motor stool.
 2. A centrifugal pump according to claim 1, wherein thewall part is formed by a tube, in which the head part is integrated by aweld connection.
 3. A centrifugal pump according to claim 1, wherein themotor stool comprises an annular flange arranged at an end of a sectionof the wall part which extends beyond the head part.
 4. A centrifugalpump according to claim 3, wherein the annular flange is configured in ashouldered manner and comprises a section which engages into an insideof the wall part and a section which lies on an end of the wall part. 5.A centrifugal pump according to claim 3, wherein the annular flange isconfigured for fastening the electric motor.
 6. A centrifugal pumpaccording to claim 5, wherein the annular flange is configured forfastening different electric motors.
 7. A centrifugal pump according toclaim 3, wherein: an attachment is formed on the annular flange andprojects in the axial direction; the attachment has an end, which isaway from the annular flange, on which a fastening flange for theelectric motor is arranged.
 8. A centrifugal pump according to claim 3,wherein at least one window is formed on the section of the wall partwhich extends beyond the head part.
 9. A centrifugal pump according toclaim 3, wherein two windows are formed on the section of the wall partwhich extends beyond the head part, said windows being arranged in amanner such that a shaft seal sealing the pump shaft with respect to thehead part, as well as at least one bleed valve of the centrifugal pump,which is arranged on the head part, are accessible via the windows. 10.A centrifugal pump according to claim 1, wherein the head part isconfigured as a deep-drawn part of preferably stainless steel.
 11. Acentrifugal pump according to claim 1, further comprising a clampingring, wherein the wall part is clamped on the foot part by the clampingring.
 12. A centrifugal pump according to claim 11, wherein the clampingring, in a peripheral direction, is configured divided into several ringsegments.
 13. A centrifugal pump according to claim 12, wherein theclamping ring comprises ring segments that are connected to the footpart amid a creation of a connection to one another.